Lock nut for electrical connectors



31, 1954 A. 1. APPLETON 2,687,757

LOCK NUT FOR ELECTRICAL CONNECTORS Filed May 3, 1950 NVBNTQ Patented Aug. 31, 1954 UNITED STATES PATENT OFF 2,687,757 I C E LOCK NUT FOR ELECTRICAL CONNECTORS Arthur I. Appleton, Northbrook, 111.

Application May 3, 1950, Serial No. 159,813

The present invention relates generally to fittings. used with electrical power supply conduits in homes, oflices and industrial buildings, but more specifically to a novel lock nut of particular utility with respect to electrical connectors.

The primary object of the present invention is to provide a novel. lock nut for fastening electrical connectors to outlet or junction boxes and which can be tightened quickly with a minimum of effort on the part of the installer.

Another object is to provide a lock nut of the character set forth and which will be susceptible of economical fabrication from heavy gauge sheet metal bymeans of mass production stamping or punching operations.

Other objects and advantages will become apparent as the following detailed description proceeds, taken in connection with the accompanying drawings, wherein:

Figure l is a perspective view illustrating a preferred form of a lock nut embodying the present. invention.

Fig. 2 is a face view of a junction box wall and showing an electrical connector secured thereto by the lock nut of Fig. 1. i i Fig. 3 is a longitudinal sectional view taken axially through the connector of Fig. 2, in the plane of the line 2-2, and showing the illustrative lock nut in gripping engagement with the junction box wall.

Fig. 4 is a side elevational view of the lock nut of Fig. 1 showing certain additional details in the formation of, the latter.

Fig. 5 is a face view of a modified form of lock nut also embodying the present invention but differing somewhat from the nut shown in Fig. 1.

While. the invention is susceptible of various modifications and alternative constructions, certain preferred embodiments have been shown in the drawings and will be described below in considerable detail. It should be understood, however, that there is no intention to limit the m vention to the specific forms disclosed, but on the contrary, the intention is to cover all modifications and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.

Conventional electrical connectors of the type mentioned above are usually formed with a threaded nose portion of appropriate size for insertion into an opening in the wall of an outlet box or junction box. In most instances, they are fastened to the box .wall, after insertion through the opening therein, by means of a suitable lock nut which compresses the marginal portion of the box wall against an abutting shoulder on the body of the connector. Lock nuts of the familiar hexagonal type as well as the toothed or serrated type have both been used for this purpose. The toothed or serrated nuts lend themselves fairly well to tightening by means of a spanner wrench and for that reason are finding wider usage in the trade than other types of lock nuts.

2 Claims. (Cl. 151-37) Current practice in the trade involves forming the serrated type lock nut as a sheet metal stamping having an internally threaded body and a seriesof circumferentially spaced, radially projecting teeth. The lateral edges of each of these teeth may either be parallel or, more. frequently, may be disposed so as to converge toward the outer periphery of each tooth. Many electricians prefer to tighten serrated or toothed lock nuts by holding the blade of a screwdriver tangentially against one of the teeth and striking the end of the screwdriver handle with the palm of the hand. Since the screwdriver is apt to slip readily off a tooth of the foregoing construction unless the installer exercises particular care, serrated lock nuts often constitute a source of petty annoyance tending to increase the cost of an electrical installation due to the additional time and effort which must be expended in tightening them.

Referring more specifically to the drawing, there is shown in Fig. l a novel illustrative lock nut in embodying the present invention and which overcomes the foregoing disadvantages.

In the present instance, the nut ii] comprises an annular body portion il in the form of a relatively short sleeve. The body H is fashioned with internal treads l2 which adapt it to engage the threaded nose I l of an electrical connector E5. As indicated. in Fig. 3, the particular conhector Hi selected for illustration happens to be designed for accommodating a flexible conduit 16 known in the trade as BX cable. The connector i5 is mounted with its threaded nose projecting through an opening [8 in the side wall l9 of an outlet or junction box 20. The marginal portion of the box wall l9 surrounding the opening it is squeezed between stub teeth 2*! of shoulder 22 ofthe connector, on the one hand, and the face of the nut ID, on the other hand. This squeezing action, of course, rigidly secures the connector in place.

Projecting in a generally radial outward direction from the body l is a gashed radial flange constituting a combined tool-engaging and locking means, such flange having a thickness substantially less than the axial dimension of the annular body H. The gashed flange has defined therein a plurality of circumferentially spaced teeth 26,, in this case six in number, the teeth 2 being disposed in alternate series relation with a plurality of convex segmental areas on the outer periphery of the annular body II. I have found that by undercutting the lateral edges of each of these teeth 24, tightening or loosening of the nut M3 by the application of axial force to a tangentially disposed screwdriver or other drivable hand tool 25 is immeasurably facilitated. Accordingly, in the presentinstance the lateral edges of the teeth 2.4..are. undercut well into the root portion of each tooth structure. These undercut lateral edgeain cooperation with the respective convex segmental areas adjacent theretadefine a pair of fulcrum pockets 26 for effecting positive pivotal engagement with the tangentially disposed screw driver 25. As indicated diagrammatically in Fig. 2, the pockets 26 of each tooth extend well within the planes of the respective radii OA and OB which are tangent to the circumferential extremities of overhanging crown portion 2! of the tooth. This gives each tooth 24 a sort of T-shaped profile with its medial portion of substantially shorter circumferential dimension than its crown portion. By reason of the foregoing undercut tooth construction, each tooth of the nut I is susceptible of snugly and pivotally engaging the end of the screwdriver 25 throughout a considerable range of angular movement of the nut. Consequently, it is ossible to tighten the nut I0 solely by means of a screwdriver in the manner described above without likelihood of slipping off the tooth.

Referring to Figs. 3 and 4, it will be perceived that each of the teeth 24 is also fashioned with a helical twist. Such twist runs in a direction opposite to that of the threads within the body I I.

As a result, when the nut is tightened the trailing end portions of the tooth crowns are pressed hard against the face of the box wall. Since the trailing end portions of the teeth are thus disposed, the force exerted by the screwdriver on individual teeth will be in a direction to maintain or even increase such tooth pressure against the face of the box wall rather than to decrease tooth pressure. Upon the application of a loosening torque to the nut, these trailing ends bite deeper into the box Wall and resist unscrewing of the nut. While mere twisting of the teeth of a serrated type lock nut may not be new, per se, I have observed that the novel construction described above provides substantially better penetration and locking action than would be obtainable with a conventional serrated nut with twisted teeth. This is due to the fact that the undercutting of the lateral edges of the teeth of the nut I0 provides sturdy and relatively sharp tutes a substantial advantage for the specific environment in which the nuts I 0, 10A are used. Since certain junction boxes and panel boxes are provided with a coat of heavy enamel to prevent rusting, this biting action efiectively breaks through the paint film to provide adequate metalto-metal contact between the connector and the box. While practically all outlet boxes presently manufactured have smooth cadium plated surfaces rather than enameled ones, the biting action above described is still advantageous.

I claim as my invention:

1. A lock nut for electrical box fittings and. the like, said lock nut comprising, in combination, a relatively short annular body having screw threads on the inner periphery thereof, a gashed radial flange on the exterior of said body and constituting a combined tool-engaging and looking means, said flange having a thickness substantially less than the axial dimension of said body, a plurality of circumferentially spaced teeth defined in said gashed flange and disposed in alternate series relation with a plurality of convex segmental areas on the outer periphery of said annular body, each said tooth having an undercut lateral edge which trails with respect to the direction in which said nut is tightened, said undercut lateral edge and the one of said convex segmental areas adjacent thereto defining a pocket for effecting positive pivotal engagement with the driving end of a screwdriver disposed generally tangentially to said body, each said tooth being twisted about a radial axis in a direction opposite to the helical run of threads in said body.

2. In a lock nut for rigidly attaching an electrical fitting to an apertured box wall or the like, the combination comprising a relatively short annular body having screw threads on the inner periphery thereof, a gashed radial flange on the exterior of said body and constituting a combined knife edges adjacent the extreme periphery of the nut. Such edges are of sufficient length to preclude mashing over but are not long enough to act as bearing areas and so inhibit penetration.

Turning now to Fig. 5, there is shown a somewhat modified lock nut IDA also embodying the present invention. The nut IDA has a body portion ll similar to that of the nut [0 but is provided with a plurality of circumferentially spaced teeth 28 also disposed in alternate series relation with a plurality of convex segmental areas but differing in profile from the teeth 24. Thus each of the teeth 28 is undercut on only one lateral edge so as to define, in cooperation with the adjacent convex segmental area, a fulcrum pocket 29 generally similar to the pockets 26. Such edge is disposed in trailing relation with respect to the direction in which the nut IDA is tightened and gives the trailing portion of the tooth a certain amount of rake. The opposite lateral edge 36 of each tooth may be substantially parallel to the edge defining the pocket 29 or may run in various other directions. The action of the undercut edges or pockets 29 upon tightening of the nut IDA by means of a screwdriver or similar tool is, of course, substantially identical with that of the undercut edges or pockets 26 of the teeth 24.

In view of the foregoing, it will be appreciated that there has been provided a novel lock nut structure which fulfills the objectives set forth earlier herein. In addition to this, the improved biting action of the teeth 24 and 28 also constitool-engaging and locking means, said flange having a thickness substantially less than the axial dimension of said body, a plurality of circumferentially spaced teeth defined in said gashed flange and disposed in alternate series relation with a plurality of convex segmental areas on the outer periphery of said annular body, each said tooth having undercut lateral edges defining, with the respective convex segmental areas adjacent thereto,-a pair of pockets for effecting positive pivotal engagement with the driving end of a screwdriver disposed generally tangentially to said body, each said tooth having a crown ortion overhanging said pair of pockets so that the latter lie well within the angular region bounded by the tangential radii from the circumferential extremities of said crown portion, each said crown portion being twisted about a radial axis in a direction opposite to the helical run of the internal threads of said body.

References Cited in the file of this patent UNITED STATES PATENTS Stellin July 10, 1951 

